Researchers at Rice University in Houston have created a bismuth-carrying nanotube that can tag stem cells for tracking and creates CT images brighter than those created using iodine-based contrast agents.

The research, published in the Journal of Materials Chemistry B, marks the first time bismuth has been combined with nanotubes to image individual cells, according to Lon Wilson, PhD, a chemist at Rice and senior author of the study.

Nanotube capsules in the study are between 20 and 80 nanometers long and 1.4 nanometers in diameter. Once they pass through the cell membrane, they clump together in masses about 300 nanometers in diameter, explained Wilson.

Dubbed Bi@ US-tubes by the research team, the bismuth-filled nanotubes have demonstrated positive results when tested on stem cells derived from pig bone marrow.

Wilson and colleagues had previously experimented with nanotube-based contrast agents for MRI before realizing the dearth of research into tracking stem cells by CT. “CT is much faster, cheaper and more convenient, and the instrumentation is much more widespread (than MRI),” Wilson said in a press release. “So we thought if we put bismuth inside the nanotubes and the nanotubes inside stem cells, we might be able to track them in vivo in real time.”

The advantage of the Bi@ US-tubes is that bismuth, being a heavy element, is more effective at diffracting x-rays than most other elements, according to Wilson. Trapping it in nanotubes also allows for the agent to be modified to target certain types of cells.

The next step for the researchers is to improve the contrast of the agent by increasing the amount of bismuth in each nanotube, and also to combine bismuth with gadolinium in one nanotube to produce a bimodal contrast agent for both MRI and CT.